1. Field of the Invention
The present invention relates to systems and methods for triggering the deployment or actuation of vehicle occupant safety devices, including particularly supplemental inflatable restraint systems such as air bags.
2. Description of the Prior Art
A variety of systems for initiating action of passive occupant safety devices for vehicles is well known in the art It bas long been recognized that the deployment decision for each of several safety devices which may be installed on a vehicle, such as airbags, safety belt pretensioners and seat pull down devices, is not one that should be based on a simple determination that a collision has occurred, but should take into account the severity of the collision, the vehicle occupants' positions and whether the vehicle occupants are using safety belts. For example, the unnecessary deployment of airbags can compromise driver control of a vehicle at a time when maintaining control is more important to avoiding injury than isolation from acceleration.
Typically, crash detection is based on a proxy device for a crash sensor, such as an accelerometer. However, for a number of reasons, raw peak acceleration measured by an accelerometer does not provide a good indication of whether a collision has occurred, or for that matter, the degree of severity of the collision. Short duration, high acceleration transients produced by road shock can generate g forces briefly comparable to g forces produced in an accident. Accordingly, acceleration signals have been subjected to filtering and threshold tests to qualify the signal as indicative of a collision involving the vehicle. Various systems have been proposed providing sophisticated mathematical treatments of acceleration, both to determine if a collision has occurred and to measure the degree of severity of the collision. U.S. Pat. No. 5,430,649 to Cashler et al., teaches a crash severity indication based on a series of treatments on basic acceleration data, which are intended to determine, among other things, whether an object which the vehicle impacted with was a pole or whether the collision occurred at a pronounced angle, i.e. the collision was a glancing one.
Crash severity is a preferred basis for the decision to deploy airbags in a collision, rather than a simple determination that a collision has occurred. However, the concept of crash severity is a somewhat nebulous one in practice. The primary object of an occupant. restraint system is to protect the occupants of the vehicle from injury. Thus crash severity should be defined in terms of the danger it poses to the occupants, and not the degree of damage to the vehicle. An accident which crushes a good deal of the front end of a vehicle may be less severe for the occupants than an accident which does not result in extensive vehicle crush. When a vehicle is crushed, much of the energy of the collision may be absorbed by the vehicle, rather than being transferred to the passenger compartment
In passenger cars, where the vehicle gross weight may well be only one or two hundred kilograms more than an empty vehicle weight of over a thousand kilograms, crush may be readily predicted by considering only vehicle deceleration (as well as its duration and the time rate of change of deceleration) caused by the impact. In commercial delivery vehicles, such as trucks, vehicle load can contribute a substantial proportion of a vehicle's gross weight and contribute to greater crush in accidents. Safety device deployment schemes devised for automobiles which discount changes in vehicle weight may not be appropriate for trucks due to the greatly varying loads carried by trucks.
What is desirable then is a safety device deployment control mechanism which can assess collision severity using selected vehicle conditions as inputs as part of a decision process relating to when and if a safety devise is deployed.